Predicting the Decline in Human Chorionic Gonadotropin in a Resolving Pregnancy of Unknown Location

Objectives To characterize the curve derived from serial human chorionic gonadotropin (hCG) values in women with spontaneous resolution of pregnancy of unknown location and to assess factors that modify the decline. Methods Data from three sites were extracted from a clinical database of women with a symptomatic pregnancy of unknown location that required follow-up with serial hCG levels. A nonlinear mixed-effects regression model was used to generate hCG elimination curves. Results Four hundred forty-three women presenting with a pregnancy of unknown location that resolved without intervention were studied between September 2007 and May 2009. Women older than 35 years had a slower hCG decline (P=.001) and those with pain had a steeper decline (P=.006), but these changes did not alter the curve in a clinically meaningful way. The decline in hCG is faster for those with a higher level at presentation. The average decline of hCG in women with spontaneous resolution is slower than previously reported. However, the minimal decline in hCG for women with spontaneous resolution of a pregnancy of unknown location ranged from 35% to 50% at 2 days of follow-up and from 66% to 87% at 7 days, which is more rapid than previously reported. Conclusion In a diverse population, using updated statistical methods, it was observed that the minimal decline in hCG for women with spontaneous resolution is more rapid than previously reported. A decline slower than these thresholds may indicate the presence of retained trophoblastic tissue or ectopic pregnancy. Level of evidence III.